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The GPS post-processing by the GAGE ACs generates tropospheric processing products which are available via ftp, organized by year and day of year. See APPENDIX G. Atmospheric Delay (*.MET) File Naming and Format of the GAGE GPS Data Analysis Plan and Products [PDF] for an explanation of the contents of these files. The tropospheric parameters are listed for each station at 2-hour intervals for New Mexico Tech and at 5-minute intervals for Central Washington University. Both ACs use the Niell Mapping Function in processing the GPS data and estimating tropospheric delays at individual sites. The Niell Mapping Function is a global grid of wet and hydrostatic delays plus a mapping function that describes the delay as a function of elevation angle of the satellite relative to the GPS receiver.

When radio waves from GPS satellites enter the neutral atmosphere they are refracted and slowed down, and the resulting delay must be accounted for in processing. The tropospheric delay has two components: the hydrostatic delay from dry gases in the atmosphere, primarily nitrogen and oxygen, and the wet delay from water vapor and condensed water (clouds).